This is why Hungary should not yet ease curbs markedly in pandemic
The herd immunity threshold (HIT), i.e. the percentage of the population protected from coronavirus via vaccination or infection, required to restrictions in place remains a subject of debate globally. There are, however, examples of cautious, gradual and risk-free re-opening tactics that give us an idea about the percentage of the population needed to be vaccinated by the time the first step is taken in this direction.
We analysed the correlation between epidemic curves and the Oxford COVID-19 Government Response Tracker, or more precisely its Stringency Index to see how the easing/tightening of lockdown measures affected the curve at various stages in the vaccination campaigns. The index shows the stringency level on 0 to 100 scale, where 0 point is no restriction measure at all and 100 is full lockdown, which has not been implemented anywhere in the world.
A brief Hungarian timeline:
- 0 – before the coronavirus outbreak in March 2020
- 10 points – no flights from Wuhan, taking the temperature of passengers arriving from Milan
- around 50 points – summer of 2020 (no mass events, mandatory mask-wearing in several closed areas)
- 40 points – September 2020 (children return to school)
- 79 points – 8 March tightening of lockdown measures (bar grocery stores, pharmacies, petrol stations, all stores and services close down temporarily, curfew, school closure, event attendance capped at 10 people, border closure, mask-wearing everywhere).
- The index peaked at 76.85 points in April.
Lockdown measures are only as good as the discipline of the population, but it’s difficult (almost impossible) to quantify therefore we assumed that most people comply with the restriction measures.
The Stringency Index in the countries under review is currently between 40 and 90 points.
The turning points (easing/tightening measures) are also marked on the charts below, as well as the percentage of the population that received at least one dose of a COVID-19 vaccine by that time. We relied on figures provided by Our World in Data.
When vaccination may have an impact
In view of international examples, we can state that we should put the spotlight on vaccination champions, as with 20% of the population inoculated against coronavirus you have no impact on the epidemic curve. This leaves us with seven to eight countries.
The first that pops in mind is Israel as the absolute leader in this respect, followed by the United Arab Emirates, but we had to be omitted because it does not have daily statistics on the number of people getting their first dose.
The Israeli example shows that the country tried to prevent the epidemic curve from sharply rising in late autumn 2020 by ever stringent lockdown measures. The gradual tightening spanned from early November to early January, and the curve started to show its impact only by mid-January 2021. The vaccination programme kicked off in mid-December, and a quarter of the population received at least their first dose by the middle of January.
We do think that it was the lockdown that brought results rather than the 25% vaccination rate for two reasons.
Firstly, a 85-point Stringency Index must make an effect on the epidemic curve sooner or later. Secondly, while the flattening of the curve suffered a setback even though vaccination campaign was still underway, which prompted authorities to tighten the screws further even while nearly 36% of the population was already vaccinated.
Protection gained via inoculation first had an impact on the epidemic curve when 40% of the population got their jabs. The downturn trend in the curve was not stopped or reversed even by a substantial easing of restriction measures.
And it’s crucial that the descent in the curve was not necessarily caused by the 40% vaccination rate. The 87pt Stringency Index was probably also behind the change, and following the peak immunity via recovery was also higher, which implies that the immunity rate was well above 40%.
Note that there was another disruption in the improvement at a 50% vaccination rate when the moderately rigorous lockdown measures proved insufficient. New momentum was gained when the 60% mark was close, and still the country maintained measures over 50 points on the Stringency Index.
Israel started to cautiously ease curbs when 40% of the country’s population was inoculated against COVID-19, and took bolder steps at 50 and 60%. What is not shown on the chart above is that the vaccination of elderly people led to a higher percentage decline in the number of people in hospital and of coronavirus victims than that in the number of new cases.
What we have seen in Chile also suggest that the epidemic curve starts to be affected (pushed lower) by vaccination once at least 40% of the population got their first jab at least. Yet, the record of these two countries is still insufficient for an unequivocal conclusion.
In Chile, a large number of cases was caused by the Brazilian variant, while most people were vaccinated by China’s Sinovac that – some studies show – is less effective against this variant. Not to mention that despite the high score on the Stringency Index Chileans remained extremely mobile and the index cannot track compliance (or non-compliance in this case) with the regulations.
We can still use Chile as a (good) example, as its lockdown measures in place since November scored as high on the Stringency Index as Hungary’s own implemented on 8 March. In early 2021, the pandemic was seemingly letting up a bit, but despite a good pace in vaccinations, the number of new cases took off in February. The pandemic is close to its peak in Chile now, the numbers have been showing a plateau since early April. This required 40% of the population to be inoculated and stringent restrictions. We have no information on the percentage of the population that gained protection via infection and there are no reliable mobility statistics either.
The example of Israel and Chile strongly suggest, however, that having 40% of the population vaccinated and strict lockdown measures in place can already exert a downward impact on the epidemic curve.
When it makes no sense to re-open relying on vaccines
Bahrein has been administering vaccines rapidly, but it has not yet inoculated 40% of the population. The epidemic curve is on a sharply ascending trajectory even with 20 to 30% of the population vaccinated against coronavirus.
This is unsurprising given that the stringency of lockdown measures is nowhere near the rigour in Israel or Chile..
In comparison to Israel and Chile you might think that the vaccination campaign has a swifter impact on the epidemic curve in Serbia. With 20% of the population vaccinated there’s a break in the curve, while restrictions are not the strictest. At the same time, the volatility seen in the trend suggest inaccuracies, an assumption apparently underpinned by the fact that policymakers implemented much stringent measures at the end of March, most likely due to the emergence of the UK variant. This tells a story of a still difficult pandemic situation.
Countries that did not leave it up to chance, and countries that did
The United Kingdom is a tough nut to crack. Despite the high ratio of the population already vaccinated against coronavirus, we can conclude absolutely no conclusion on the early impact of the vaccination campaign on the spread of coronavirus, as lockdown measures were extremely strict almost throughout the year.
The score of 88 on the Stringency Index is outstanding therefore it comes as no surprise that it brought about a steep drop in the epidemic curve even though B.1.1.7, which was first detected there, was spreading fast. The easing in February took the index only to 86 points, and the flattening of the curve in March almost certainly stems from the ironclad restrictions (the drop started when only a small percentage of the population was vaccinated against SARS-CoV-2). Hence, we have no way of telling what impact vaccines had on the epidemic curve until the end of March. Great Britain was able to afford a slight easing of the curbs to 76 points once it had 40 to 45% of the population inoculated, yet downward curve became steeper.
The British example also suggests that this could be the vaccination rate at which a palpable impact on the epidemic curve can be detected.
The occurrence of B.1.1.7 brought a whole new situation to the United States, as well. At least it appears that the stringency that proved sufficient to curb the spread of the virus in early 2021 is no longer doing the job. The cautious re-opening was followed by an accelerated spread of the virus even though 30% of the population have had at least their first dose of a COVID-19 vaccine.
Vaccines are clearly not the reason why the epidemic curve turned down from the peak. What facilitated the improvement was the lockdown measures scoring around 70 points on the Stringency Index and the high ratio of immunity by recovery (the rolling 7-day average of new daily cases was around 250,000 at the peak). As you can see, when the stringency of restrictions was lowered to 68 points, the steepness of the epidemic curve did not change for a couple of weeks, but then it reached a plateau and over the past few days the number of new daily confirmed cases has started to rise slightly again, while 30% of the population received their first jab.
The sharp decline in new confirmed cases in early 2021 is clearly attributable to lockdown measures, and once they were eased the deceleration of the spread of the virus balked, regardless of the fact that almost a third of the population got inoculated.
We also need to know that the Stringency Index gauges the measures of the federal government, while a lot stricter restrictions were implemented in coronavirus hotspots that managed to stifle the spread of the virus locally. Vaccines most likely contributed to the downturn in the epidemic curve to some extent but vaccination was not the facilitator of the change. Vaccination was also unable to pull the country out of the plateau with a Stringency Index score of 60 to 65.
We should revisit the USA once 40% of the population is vaccinated and see how the epidemic curve is doing then, given that where there was a break in the curve (Chile, Israel, United Kingdom), the Stringency Index score was north of 70 points.
What about Hungary?
In Hungary, 30% of the population has been vaccinated against COVID-19 with the first dose (Our World in Data reported 28.6% on 9 April), which makes it one of the best in the world. While the daily number of new confirmed cases might suggest that the pandemic is in retreat, and the positivity rate has been dropping too (although the volatility in the number of tests performed remains huge), based on international examples we can say it with a high degree of certainty that there’s no strong correlation between vaccination and (potentially) improving epidemiological data.
The turnaround in the rolling 7-day average of new daily cases came about when only 18.7% of the population had their first jab. Nowhere it the world did the trend turn around at such a low vaccination rate. The impact must have come mainly from the closure of schools on 8 March, not to mention that the statistics paint a more favourable picture than reality, given that the number of tests dropped drastically for four to five days due to Easter. The pandemic is petering out but the actual epidemic curve is almost certainly not as steep as the official one. The easing measures of last week have not yet been quantified, but we estimate that they now score between 70 and 75 points on the Stringency Index. This coupled with 30 to 40% of the population inoculated against coronavirus would not necessarily entail a break in the descending trend, but further easing of the curbs without having at least 40% of the population vaccinated would be risky in view of global examples.
We do not yet see clearly
Summing up the lessons we have (or should have) learned from the strategies and statistics of various countries we can state that when 40% of the population is vaccinated against SARS-CoV-2 the spread of coronavirus can already be impacted by this. However, re-opening needs to be gradual even in this case, no country should go all the way at lifting lockdown measures with only 40% of the population protected from the virus.
A high percentage of the population needs to be inoculated because most countries started their vaccination programmes with the elderly population, i.e. the correlation between the vaccination rate and the decline in the number of contacts is not linear. Our conclusions are cautious for a couple of reasons, though:
- The occurrence of B.1.1.7 created a whole new situation. The stringency of lockdown measures that proved (or would have proven) sufficient last year in the second wave will no longer suffice, but the UK variant is not present to the same degree in every country.
- The Stringency Index shows the theoretical strictness of anti-coronavirus measures but people’s compliance with the rules can affect it significantly and it cannot be gauged.
Cover photo: Getty Images