The Covid-19 vaccines developed by AstraZeneca, Moderna, and Pfizer–BioNTech, and others are proving effective in preventing ‘symptomatic’ disease, but it is still uncertain how well they protect people from becoming infected, or from spreading the virus to others.
A small percentage of people who are fully vaccinated are still getting Covid-19 if they are exposed to the virus that causes it. These are called ‘vaccine breakthrough’ cases. This means that while people who have been vaccinated are much less likely to get sick, it may still happen. Research is on-going about how common these cases are.
In the United States, a country with the most vaccinated people, the Centre for Disease Control (CDC) on 15 April reported that it has identified close to 5,800 confirmed cases of Covid-19 among the fully vaccinated people. Of those infected, 396 (7%) required hospital admission and 74 (1%) died.
It is important to note that asymptomatic breakthrough cases may not be reported, since routine testing may not be done among those already vaccinated. Deaths among the vaccinated population in the US as of mid-April is 0.008 percent of the total inoculated population. This is an extremely low number.
The bottom line here is that vaccines work very well against the most dominant variants in the US, but such benefits are reduced with less common variants. In a cohort of 417 persons in Rockefeller University Hospital, who had received the second dose of BNT162b2 (Pfizer–BioNTech) or mRNA-1273 (Moderna) vaccine at least two weeks previously, two women with vaccine breakthrough infection were identified.
In a study in Israel, 170 SARS-CoV-2 infections among health care workers between 19 December, 2020 and Jan 24, 2021, 58% reported symptoms and were designated as Covid-19 cases. Of the 170 HCWs who were infected, 52% were unvaccinated, 46% tested positive after the first dose, and 2% tested positive after the second dose.
This suggests that though the risk of infection remains a small percentage of the vaccinated population, it is significantly reduced two weeks after the final dose. Even among vaccinated people who test positive, there is evidence that severity and fatality are rare.
What is happening in India will have direct impact on us in Nepal. There, the emergence of the term double mutant coincided with a massive increase of Covid-19 cases and deaths in India. It is not proven, but there is a broad consensus that these new mutations are more contagious, and likely cause more severe symptoms. But the most important question is whether the mutant or other unknown mutants in India are able to evade vaccine immunity.
The answer is: we do not know. The Indian Council of Medical Research (ICMR) has data that shows 4,208 people who had taken the first dose of the Bharat Biotech Covaxin tested positive for coronavirus—this 0.04% of the 9,356,436 people vaccinated.
This is a clever way of presenting data as all those who are vaccinated do not have the same level of exposure. That is why there needs to be a comparison group which there is not. The ICCMR also reports that 100,302,745 people in India have received the first dose of the Covishield vaccine and 17,145 have tested positive after that, which is 0.02%. That does not mean taking only one dose is better than taking two doses. Based on this data the percentage of positive cases among those who have received one dose is lower than those who have received both.
There have been reports in the Indian media that 10% of the new hospitalisations there is among those who have received at least one dose of a vaccine. Being so close to India, and with many people going back and forth across the open border, the vaccinated population in Nepal must take precautions: maintain distance, avoid crowds and wear a mask when out for at least a month or two.
Meanwhile, AstraZeneca has sent the Serum Institute India a legal notice over delays in the vaccine supply and has threatened to cancel its production agreement. Serum Institute is planning to declare that it will not be able to meet its obligation to supply Covishield due to domestic demand.
This has resulted in delays in delivery to all major countries, including Nepal which was planning to extend its Covishield vaccination drive through direct purchase and under the COVAX initiative.
India is starting to vaccinate every one above 18 from 1 May. Currently, the Serum Institute is producing about 2 million doses a day and is likely to take a year or more just to meet Indian demand.
All this means that those have been vaccinated should consider themselves extremely lucky. There will not be many (or any) vaccines available when the second wave peaks in Nepal.
Data so far is actually quite encouraging about the protection that vaccines give, and the time will soon come when a sense of normalcy will return–being able to sit around and have coffee with vaccinated friends or family two weeks after the second dose.
Masks, however, are going to be part of our lives for many years to come, as reaching a herd-immunity threshold is looking quite unlikely because of vaccine hesitancy, the emergence of new variants, and the delayed arrival of vaccines for children.
Sushil Koirala is a public health expert with 23 years of international experience with USAID, UNDP, the Global Fund, and has worked as a technical adviser to the Nepal Ministry of Health.