the effectiveness of single-dose vaccines

The Federal Health Council approved this Friday A recommendation which provokes a debate: postpone the application of the second dose of the vaccine against the coronavirus. Now, each jurisdiction must decide whether or not to apply it. The province and city had already agreed that this was a practical strategy at this time of the pandemic.

The proposal by the Minister of Health, Carla Vizzotti, was supported by those responsible for the provincial health portfolios. The goal, given the global shortage of vaccines, is to give a first dose to more people so that they can have a higher percentage of the population at risk vaccinated in the face of the onset of low temperatures, which have a double negative effect on the pandemic. On the one hand, the cold is more beneficial for the virus but it also reinforces the behaviors that generate its spread.

For it, the new strategy could be summed up in a less is more. But the vaccines, at least the three that are applied in Argentina, were designed to meet a two-dose schedule. Do they serve the same thing then with just one dose? How effective is a single application?

Infectologists consulted by Bugle they stress that what can be done is to defer and not to suspend the application of the second. In other words, extend the period until the second dose is given. “Vaccines have to stay on their full schedule,” said Roberto Debbag, vice president of the Latin American Society of Pediatric Infectious Diseases, who considered the possibility of vaccinating more people with a single dose because in this scenario the Argentina is far from meeting the ideal.

This Friday, with the arrival of a new load of Sputnik V, Argentina will have received 5 million doses of vaccines and 218,000 AstraZeneca units from the first batch of the COVAX fund are expected to arrive on Sunday. In December, official forecasts estimated that a good chunk of the 12 million people in risk groups had already been vaccinated by this time of year: so far, according to the Vaccination Monitor, 2.8 million people received one dose and 650,000 received two.

Dosage and protection

How protected are some and how well are others? You must see one vaccine by vaccine. First, we have already said, vaccines that are applied in the country, in two developments (that of the Swedish-British laboratory AstraZeneca and the Chinese Sinopharm) both components are the same and the second enhances the immunization of the first. In Russian Sputnik V, these are two different components for which cannot be traded.

In the case of Sputnik, efficacy reaches 87% after 14 days after receiving the first dose, and rises to 91% after receiving the second dose, which is indicated on the 21st day of the first, ideal period of application although the Gamaleya declared – which had also already been declared by the former minister Ginés González García – that it could be extended to two months. However, the government also recommended to postpone it to a minimum interval of 12 weeks from the first dose.

Regarding AstraZeneca, the efficacy with the first dose is 76%. These figures are what decided the UK government to postpone the application of the second dose to postpone the second dose until the fall. Ten days ago, in a virtual meeting with Vizzotti, UK COVID-19 Vaccine Deployment Minister Nadhim Zahawi assured that only 3% of the country’s population was vaccinated with the full regimen and this only with the first dose hospitalizations and deaths have been reduced by 90%.

On this vaccine, there is data that also encourages postponement, and that they had already anticipated Bugle as a strategy in the city: administering the second dose later was found to increase efficiency. When received 14 days after the first, protection was 63%, but when received at 12 weeks or more, it was 82%. This applies to AstraZeneca and Covishield vaccines, which are the same as those produced in India.

Sinopharm doubts

And that of Sinopharm? There would be a problem here, at least one of communication. As with Sputnik earlier this year, the results of the phase III trial of the Chinese vaccine have not yet been published in any scientific journal. The vaccine is known to be 79% effective with two doses 21 days apart, but it has not been publicly disclosed what levels it reaches with a single dose.

These data refer to the overall effectiveness of vaccines, which has to do with the ability to avoid contagion. Regarding the effectiveness related to the prevention of serious diseases, the values ​​are higher: as infectologist Eduardo López explained to this journal, all have in common an effectiveness of more than 95% against serious diseases.

“It’s fundamental, but that’s not why it should be neglected. Thinking in particular of the one who has not yet been vaccinated, ”said López, who stressed the importance of maintaining social distance, the use of a chin strap and hand washing.

AS