Covid: how will the application of the second dose be faced in the absence of vaccines

According to the open database of Ministry of Health, until this morning, 8,533,232 had been applied in the country dose of vaccines against Covid-19 which made it possible to vaccinate with at least one dose approximately 75% of those over 80, 83% of adults between 70 and 79 years, 63% of those between 60 and 69 years, 16% of those between 50 and 59 years and 11 % from 40 to 49. In other words, over 70% of those over 60 received their first dose.

According to the estimates of the biochemist specializing in data analysis Santiago olszevickiIf minors are excluded and only the adult population is taken into account, this coverage reaches 23.5%.

Leaving aside the team of Health and others essential workers (who for the most part have already received the full program), several of the first to be vaccinated in mid-February are already turning 90 days after Pause who should mediate between the first and the second dose, and they see with some concern the difficulties access vaccines.

The India has already announced that it has suspended exports of Covishield, prepared by agreement with the company AstraZeneca; the Instituto Gamaleya it is not enough to meet the demand for your vaccine Sputnik V and deliver items smaller than those incurred; and the Anglo-Swedish formula, Oxford-AstraZeneca, whose active substance is manufactured in our country, has not yet sent any of those agreed under the agreement signed with the Slim Foundation, of Mexico. Finally, although the promised four million doses of the vaccine were received from Sinopharm, there is no guarantee that more can be acquired.

However, Juan Manuel Castelli, national director of Fight against immuno-preventable diseases, puts cold rags: “Those who received Covishield, because it is exactly the same vaccine that AstraZeneca markets, but with a different name, can perfectly receive the second dose of the latter – reassures -. It’s made explicit in the technical guidelines we released in March, when both were available in the country. Regarding Sinopharm, on April 23, we published a press release specifying that from that day on, all the new doses (two million) that arrived were going to be used to supplement the schedules of those who had received the first. This is already done by most jurisdictions ”.

Castelli specifies that, although since mid-March, the strategy of prioritization of first dose (ie vaccinate more people with one and postpone the application of the second), the government is working to get them in “component secondss ”and thus be able to complete the diagrams.

“Initially, the minimum interval of 90 days is respected,” he says. But this period is not exhaustive, it can be 92, 93, 95 … If we take vaccines developed with another platform, as in the case of Canada, the minimum interval was set at four months. The prioritization strategy is based on the effectiveness obtained by the first dose, which is the one that awakens the patient. immune response. The second thing it does is increase the efficiency and extend it. In the case of AstraZeneca, it has been shown that it is possible to go from 70% efficiency in four weeks to 80% with a minimum interval of two months. And in Sputnik, there are already local studies that report high efficacy after the first dose. “

The effectiveness after one and two application doses results from the clinical tests. Yesterday, it was reported that Sinopharm is around 65% after the first (between 18 and 59; there is no data for people over 60) and 78% after the second. Regarding Sputnik V, according to data from its phase III study published in The Lancet, 21 days after the first dose, it shows 91.6% with both. There is no clinical follow-up data for a single dose, but a study carried out in the province of Buenos Aires showed the presence of antibodies in 94% of people after the first application. According to the president of the Argentine Society of Infectology, Omar Sued, this latest work is worth knowing that it is highly immunogenic, but the effectiveness is measured in “percentage of protection” compared to the control group. “We believe that a single dose is as effective as two (at least in the short term), but we have no concrete evidence,” he says.

AstraZeneca has conducted clinical trials in different countries (South Africa, United Kingdom and United States) and the effectiveness is not exactly the same in all: about 60% after the first dose and 72% with two, but the latter increases when they are three months apart. However, when it comes to preventing serious illness and the death for him novel coronavirus, the effectiveness of most vaccines exceeds 95%.

“The UK example is overwhelming – highlights Daniela Hozbor, coordinator of the vaccination subcommittee of Argentine Association of Microbiology and principal investigator of the Conicet-. He took the measure of vaccinating with a single dose when he had on average more or less 60,000 cases daily and nearly 2,000 deaths. And it comes down to almost 5,000 cases and hundreds of deaths. Today, it has 2,000 cases and less than 50 deaths per day. The second dose strengthens and improves the quality of the immune response and prolongs it over time. What is stipulated between one dose and another is the minimum time, not the maximum. Because if you gave the second one a week after the first, it wouldn’t get the desired beneficial effect. We must wait until there is a proliferation of lymphocytes, so that the population of immunological memory appears … A time which is generally four weeks. And the answer is not weakened if you wait a little longer ”.

About the possibility of combine vaccinesBoth Castelli and Hozbor say the results of ongoing studies are to be awaited.